Timing synchronization methods and apparatus

ABSTRACT

Various methods and apparatus are directed to achieving timing synchronization and propagating timing information pertaining to an external, e.g., non Wi-Fi, timing signal source. In some embodiments, a mobile communications device receives and processes a timing signal, e.g., a first Wi-Fi beacon, which is propagating timing information about an external timing signal from a device which directly received the external timing signal. Thus, a mobile wireless communications device achieves timing synchronization with respect to an external timing signal which it is unable to receive directly. In various embodiments, the mobile communications device may, and sometimes does, further propagate the timing information about the external timing signal, e.g., via a second Wi-Fi beacon signal which it generates and transmits. Synchronization with respect to an external signal source facilitates longer sleep states and decreased power consumption.

FIELD

Various embodiments relate to wireless communications, and moreparticularly, to methods and apparatus for synchronizing mobilecommunications devices.

BACKGROUND

WiFi chips typically draw a lot of current while in use, making itinfeasible to run certain kinds of WiFi applications using existingmethods on cellular devices. Even though certain power saving featureshave been proposed, generally they remain inefficient in terms of powerconsumption to run WiFi applications on a cellular device, even when thedevice is in passive mode, without significantly impacting the standbytime. Examples of such power intensive applications include peerdiscovery, routing information exchange, and traffic monitoring. Part ofthe power consumption problem relates to the relatively low level ofsynchronization in Wi-Fi systems and the relatively high amount of timeneeded to monitor for activity from other devices. If higher levels ofsynchronization could be achieved, monitoring time could be reduced,sleep time could be increased, and power consumption could be reduced.Based on the above discussion there is a need for methods and apparatusfor increasing timing synchronization and thus potentially reduce devicepower consumption, e.g., by increasing the amount of sleep time comparedto less synchronized devices.

SUMMARY

Exemplary methods and apparatus related to timing synchronization in awireless communications system are described. Various methods andapparatus are well suited for supporting efficient peer to peer networksoperating in unlicensed frequency spectrum. Various methods andapparatus are directed to the propagation of timing informationpertaining to an external timing source. Some embodiments are wellsuited to wireless communications systems in which devices withdifferent capabilities are deployed. For example, some devices, e.g.,high end devices, in the system may include an external timing signalreceiver, e.g., a GPS receiver, for receiving a timing signal from a nonWi-Fi device. Other devices, e.g., low end devices, may not include theexternal signal receiver for receiving a timing signal from a non Wi-Fidevice. Exemplary methods and apparatus facilitate synchronization withrespect to the external signal source by devices lacking a receiversupporting the type of signals transmitted by the external signalsource.

In some embodiments, a mobile wireless communications device achievestiming synchronization with respect to an external timing signal, e.g.,a global timing signal, which it is unable to receive directly, e.g.,the external timing signal is a GPS signal and the mobile wirelesscommunications device does not include a GPS receiver. In someembodiments, the mobile communications device receives and processes atiming signal, e.g., a first Wi-Fi beacon, which is propagating timinginformation about the external timing signal, e.g. GPS signal. Invarious embodiments, the mobile communications device may, and sometimesdoes, further propagate the timing information about the external timingsignal, e.g., via a second Wi-Fi beacon signal which it generates andtransmits. Thus an extended network, synchronized to the external timingsignal is formed, including both devices which are able to directlyreceive the external timing signal and those which are not able todirectly receive the external timing signal.

An exemplary method of operating a first mobile communications deviceoperating in an unlicensed frequency band, in accordance with someembodiments, comprises: while operating in a first mode of operation,receiving a timing signal of a first type from a second mobilecommunications device, said first type of timing signal beingsynchronized to a global timing signal source, and synchronizing aninternal clock based on the received timing signal from the secondmobile communications device. The exemplary method, in some embodiments,further comprises after synchronizing the internal clock, switching to asecond mode of operation wherein sleep state intervals in said secondmode of operation are longer in duration than sleep state intervals insaid first mode of operation.

A first mobile communications device, in accordance with someembodiments, comprises: at least one processor configured to: receive atiming signal of a first type from a second mobile communications devicewhile operating in a first mode of operation, said first type of timingsignal being synchronized to a global timing signal source, synchronizean internal clock based on the received timing signal from the secondmobile communications device, and switch to a second mode of operationwherein sleep state intervals in said second mode of operation arelonger in duration than sleep state intervals in said first mode ofoperation, after synchronizing the internal clock. The first mobilecommunications device further comprise memory coupled to said at leastone processor.

In some, but not necessarily all embodiments, propagation of timingsynchronization signals is performed based on available battery power,the source of the signal upon which the timing signal to be propagatedis based and the number of timing signals, e.g., beacon signals,detected in a given time period.

While various embodiments have been discussed in the summary above, itshould be appreciated that not necessarily all embodiments include thesame features and some of the features described above are not necessarybut can be desirable in some embodiments. Numerous additional features,embodiments and benefits of various embodiments are discussed in thedetailed description which follows.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a drawing of an exemplary wireless peer to peer communicationssystem in accordance with an exemplary embodiment.

FIG. 2 is a drawing illustrating an example in which an externalsynchronization source is used in exemplary peer to peer system of FIG.1 to provide a high level of synchronization among peer to peer devices.

FIG. 3 is a drawing illustrating another example in which an externalsynchronization source is used in exemplary peer to peer system of FIG.1 to provide a high level of synchronization among peer to peer devices.

FIG. 4 is a drawing illustrating another example in which an externalsynchronization source is used in exemplary peer to peer system of FIG.1 to provide a high level of synchronization among peer to peer devices.

FIG. 5 is a first part of a flowchart of an exemplary method ofoperating a first mobile communications device operating in anunlicensed frequency band in accordance with an exemplary embodiment.

FIG. 5B is a second part of a flowchart of an exemplary method ofoperating a first mobile communications device operating in anunlicensed frequency band in accordance with an exemplary embodiment.

FIG. 5C is a third part of a flowchart of an exemplary method ofoperating a first mobile communications device operating in anunlicensed frequency band in accordance with an exemplary embodiment.

FIG. 5D is a fourth part of a flowchart of an exemplary method ofoperating a first mobile communications device operating in anunlicensed frequency band in accordance with an exemplary embodiment.

FIG. 5E is a fifth part of a flowchart of an exemplary method ofoperating a first mobile communications device operating in anunlicensed frequency band in accordance with an exemplary embodiment.

FIG. 6 is a drawing of an exemplary mobile communications device, inaccordance with an exemplary embodiment.

FIG. 7 is an assembly of modules which can, and in some embodiments is,used in the mobile communications device of FIG. 6.

FIG. 8 shows an exemplary timing structure used by an exemplary mobilecommunications device in a first mode of operation in which the mobilecommunications is not synchronized with respect to a global timingsource and a different exemplary timing structure used by the exemplarymobile communications device in a second mode of operation in which themobile communications is synchronized with respect to a global timingsource.

FIG. 9 is a table listing different exemplary timing signals that areused in some exemplary embodiments to communicate timing synchronizationinformation.

FIG. 10 is drawing illustrating an exemplary format of an exemplarytiming signal, e.g., a Wi-Fi compliant beacon.

FIG. 11 illustrates an exemplary external timing signal source, a firstpeer to peer network which is synchronized with respect to the externaltiming signal source, a second peer to peer network which is notsynchronized with respect to the external timing signal source, and athird peer to peer network which is not synchronized with respect to theexternal timing synchronization source.

FIG. 12 illustrates the propagation of external timing signal sourcetiming information via beacons.

FIG. 13 illustrates an expanded peer to peer network which mobilecommunications devices without an external signal source receiver aresynchronized with respect to the external timing signal source.

DETAILED DESCRIPTION

FIG. 1 is a drawing of an exemplary wireless peer to peer communicationssystem 100 in accordance with an exemplary embodiment. Exemplarywireless peer to peer communications system 100 includes a plurality ofwireless communications devices (device 1 102, device 2 104, device 3106, device 4 108, device 5 110, device 6 112, device 7 114, . . . ,device N 116. Some of the wireless communications devices in system 100,e.g., device 4 108 and device 7 114 include an interface (118, 120),respectively, to the Internet and/or other network nodes. Some of thewireless communications devices in system 100, e.g., device 1 102,device 2 104, device 3 106, device 4 108, device 5 110, device 6 112,device 7 114, and device N 116, are mobile wireless communicationsdevices, e.g., handheld mobile devices. Some of the communicationsdevice in system 100, e.g., device 2 104, device 4 108, and device 6112, include an external synchronization source receiver module (128,130, 132), respectively. Other communications devices in the system 100,e.g., device 1 102, device 3 106, device 5 110, device 7 114 and deviceN 116, do not include a module for achieving synchronization directlyfrom the external synchronization source.

In some embodiments, the external synchronization source signal is a GPSsignal, e.g., from one or more GPS satellites (GPS satellite 1 122, . .. . , GPS satellite N 124). In some embodiments, the externalsynchronization source signal is a terrestrial external synchronizationsource signal, e.g., a eLORAN signal or a LORAN-C signal, or CDMA 2000signal or WWVB signal or DTV signal or LTE signal. Exemplary node 126 isan exemplary terrestrial synchronization source. In some embodiments,the external synchronization source may be located on water, e.g.,situated on a platform or located in a water vehicle. In someembodiments, the external synchronization source may be located in theair, e.g., situated in an air vehicle.

FIG. 2 is a drawing 200 illustrating an example in which an externalsynchronization source is used in exemplary peer to peer system 100 ofFIG. 1 to provide a high level of synchronization among peer to peerdevices. This allows peer to peer devices to reduce monitoring intervalsand increase sleep time, e.g., resulting in reduced battery consumption.In this example, GPS satellites (122, 124) transmit GPS signals (202,204), respectively. Device 2 104 includes an external synchronizationsource receiver module, e.g., a GPS processing module. Externalsynchronization source receiver module 128 of device 2 104 receives GPSsignals (202, 204) and determines synchronization with respect to a GPStime reference. Device 2 104 generates and transmits beacon signal 206which communicates timing synchronization information. Beacon signal 206also communicates information 208 indicating that the timingsynchronization information being communicated in beacon signal 206 isbased on direct GPS reception.

Transmitted beacon signal 206 is detected by device 3 106. Device 3 106achieves a high level of timing synchronization based on timinginformation communicated by beacon 206. Device 3 106 generates beaconsignal 210 communicating timing synchronization information. Beaconsignal 210 also communicates information 212 indicating that the timingsynchronization information being communicated in beacon signal 210 isbased on a received relay synchronization beacon, e.g., secondhandinformation.

Beacon signal 210 is received and recovered by device 1 102 and device N116. Devices (102, 116) use the timing synchronization informationcommunicated by beacon signal 210 to achieve a high level of timingsynchronization. Devices (102, 116) recover the information 212indicating that the device which generated beacon signal 212 did notdirectly receive the GPS signal on which the timing synchronization isbeing based. Therefore devices (102, 116) do not generate and transmitbeacon signals to further propagate the timing synchronizationinformation.

Device 5 110 also receives and recovers beacon signal 206. However,device 5 110 has been monitoring its battery status and its currentbattery status=low as indicated by block 214. Therefore device 5 110decides not to generate and transmit a beacon signal to propagate timingsynchronization information. In this way, device 5 110 conserves itsremaining battery energy.

Device 7 114 also receives and recovers beacon signal 206. However, thereceived beacon signal power level is high, e.g., above a predeterminedthreshold, as indicated by block 216. Therefore device 7 114 decides notto generate and transmit a beacon signal to propagate timingsynchronization information. Device 7 114 expects that there would besubstantial overlap, with regard to coverage range, with beacon 206, ifdevice 7 114 were to transmit a beacon. Thus device 7 114 does not wasteits battery energy by transmitting an unnecessary beacon.

FIG. 3 is a drawing 300 illustrating another example in which anexternal synchronization source is used in exemplary peer to peer system100 of FIG. 1 to provide a high level of synchronization among peer topeer devices. In this example, GPS satellites (122, 124) transmit GPSsignals (202, 204), respectively. Device 2 104 includes an externalsynchronization source receiver module, e.g., a GPS processing module.External synchronization source receiver module 128 of device 2 104receives GPS signals (202, 204) and determines synchronization withrespect to a GPS time reference. Device 2 104 generates and transmitsbeacon signal 206 which communicates timing synchronization information.Beacon signal 206 also communicates information 208 indicating that thetiming synchronization information being communicated in beacon signal206 is based on direct GPS reception by device 2 104.

Transmitted beacon signal 206 is detected by device 3 106, device 5 110,device 7 114 and device N 116. Device 3 achieves a high level of timingsynchronization based on timing information communicated by beacon 206.Device 3 106 generates beacon signal 310 communicating timingsynchronization information. Beacon signal 310 also communicatesinformation 312 indicating that the timing synchronization informationbeing communicated in beacon signal 310 is based on a received relaysynchronization beacon, e.g., secondhand information. In someembodiments, a device which decides to transmit a timing synchronizationbeacon, selects a time interval in a recurring timing structure totransmit its beacon which complements other beacons which are alreadybeing transmitted. For example, device 3 may select to transmit itsbeacons at predetermined intervals which are non-overlapping with thoseof beacon 206 from device 2 104.

Device N 116 achieves a high level of timing synchronization based ontiming information communicated by beacon 206. Device N 116 generatesbeacon signal 311 communicating timing synchronization information.Beacon signal 311 also communicates information 313 indicating that thetiming synchronization information being communicated in beacon signal311 is based on a received relay synchronization beacon, e.g.,secondhand information. In some embodiments, a device which decides totransmit a timing synchronization beacon, selects a time interval in arecurring timing structure to transmit its beacon which complementsother beacons which are already being transmitted. For example, device 3106 may select to transmit its beacons at predetermined intervals whichare non-overlapping with those of beacon 206 from device 2 104.

Device 5 110 has been monitoring its battery status and its currentbattery status=low as indicated by block 214. Therefore device 5 110decides not to generate and transmit a beacon signal to propagate timingsynchronization information. In this way, device 5 110 conserves itsremaining battery energy.

At device 7 114, the received beacon signal power level corresponding tothe beacon 206 is high, e.g., above a predetermined threshold, asindicated by block 216. Therefore device 7 114 decides not to generateand transmit a beacon signal to propagate timing synchronizationinformation. Device 7 114 expects that there would be substantialoverlap, with regard to coverage range, with beacon 206, if device 7 114were to transmit a beacon. Thus device 7 114 does not waste its batteryenergy by transmitting an unnecessary beacon.

FIG. 4 is a drawing 400 illustrating another example in which anexternal synchronization source is used in exemplary peer to peer system100 of FIG. 1 to provide a high level of synchronization among peer topeer devices. In this example, terrestrial external synchronizationsource 126, e.g., an eLORAN or LORAN-C or CDMA 2000 or WWVB signal orDTV signal or LTE signal source, transmits external synchronizationsignal 402. For purposes of this example, consider that signal 402 is aLORAN-C signal.

Device 2 104 includes an external synchronization source receiver module128. External synchronization source receiver module 128 of device 2 104receives external synchronization signal 402 and determinessynchronization with respect to the LORAN-C reference. Device 2 104generates and transmits beacon signal 406 which communicates timingsynchronization information. Beacon signal 406 also communicatesinformation 408 indicating that the timing synchronization informationbeing communicated in beacon signal 406 is based on direct reception ofa LORAN-C signal by device 2 104.

Device 4 108 includes an external synchronization source receiver module130. External synchronization source receiver module 130 of device 4 108receives external synchronization signal 402 and determinessynchronization with respect to the LORAN-C reference. Device 4 108generates and transmits beacon signal 408 which communicates timingsynchronization information. Beacon signal 408 also communicatesinformation 410 indicating that the timing synchronization informationbeing communicated in beacon signal 408 is based on direct reception ofa LORAN-C signal by device 4 108.

Device 6 112 includes an external synchronization source receiver module132. External synchronization source receiver module 132 of device 6 112receives external synchronization signal 402 and determinessynchronization with respect to the LORAN-C reference. Device 6 112generates and transmits beacon signal 412 which communicates timingsynchronization information. Beacon signal 412 also communicatesinformation 414 indicating that the timing synchronization informationbeing communicated in beacon signal 412 is based on direct reception ofa LORAN-C signal by device 6 112.

Transmitted beacon signals (404, 408, 412) are detected by device 1 102.Device 1 102 achieves a high level of timing synchronization based ontiming information communicated by beacons (404, 408, 412). Device 1 102determines that the number of received timing synchronization signalswhich were generated based on direct reception of an externalsynchronization signal is three, as indicated by box 416. Device 1 102makes a decision whether or not to transmit a timing synchronizationbeacon as a function of the determined number of received timingsynchronization signals which were generated based on direct receptionof an external synchronization signal. In this example, consider thatwhen the determined number is greater than or equal to 3, device 1 102decides to refrain from transmitting a timing synchronization beacon, soin this example, device 1 102 does not transmit a timing synchronizationbeacon. The rationale for this approach is that there is a sufficientnumber of timing synchronization beacons based on direct reception of anexternal signal source in the vicinity of device 1 102 to support thetransfer of timing synchronization information to other devices in thevicinity which do not include an external synchronization source receivemodule. If device 1 102 were to generate and transmit a timingsynchronization beacon, the timing synchronization informationcommunicated would secondhand timing information. The timingsynchronization information from a relay type beacon from device 1 102,in general, would be less accurate that from a beacon generated based ondirect reception of the external timing signal. In addition, a beaconfrom device 102 would occupy valuable air link resources with little orno potential benefit.

Transmitted beacon signal 412 is detected by device N 116. Device N 116achieves a high level of timing synchronization based on timinginformation communicated by beacons 412. Device N 116 determines thatthe number of received timing synchronization signals which weregenerated based on direct reception of an external synchronizationsignal is one, as indicated by box 417. Device N 116 makes a decisionwhether or not transmit a timing synchronization beacon as a function ofthe determined number of received timing synchronization signals whichwere generated based on direct reception of an external synchronizationsignal. In this example, consider that when the determined number isgreater than or equal to 3, device N 116 decides to refrain fromtransmitting a timing synchronization beacon. So in this example, deviceN 116 generates and transmits a timing synchronization beacon 418.Beacon 418 includes information 420 indicating that the source of thetiming synchronization beacon is a received relay synchronization beaconand not direct reception of the external synchronization signal 402 bydevice N 116.

Device 5 110 receives beacon signal 418. Device 5 110 achieves a highlevel of timing synchronization based on timing information communicatedby beacons 418. Device 5 110 recovers the information 420 from beaconsignal 418 indicating that beacon signal 418 is based on a receivedrelay synchronization beacon. In such a scenario device 5 determines notto generate and transmit a timing synchronization beacon. In general, ina relay process of communicating timing synchronization information,degradation in the level of timing synchronization information withrespect to the external source may be expected for each stage. In thisexample, the first device in the chain, once removed from directreception of the external synchronization signal, is conditionallyallowed to transmit a timing synchronization beacon. However, a devicetwice in the chain is not permitted to further propagate the timingsynchronization information in a beacon signal.

In some other embodiments, a higher level of propagation of timingsynchronization is allowed. For example, in one such embodiment, adevice twice removed from direct reception of the external timingsynchronization source is also conditionally permitted to transmit atiming synchronization beacon signal, but a device three times removedfrom direct reception of the external timing synchronization signal isnot allowed to further propagate timing synchronization information. Insome such embodiments a timing synchronization beacon communicatesinformation indicating whether the timing synchronization beacon wasgenerated by a device which directly received the externalsynchronization signal or whether it is based upon relayed timingsynchronization information. In some such embodiments, a timingsynchronization beacon further communicates, when the beacon is basedupon relayed timing synchronization information, a level of distancefrom the external synchronization source, e.g., once removed or twiceremoved.

FIG. 5, comprising the combination of FIG. 5A, FIG. 5B, FIG. 5C and FIG.5D, is a flowchart 500 of an exemplary method of operating a firstmobile communications device operating in an unlicensed frequency bandin accordance with an exemplary embodiment. Operation starts in step502, where the first communications device is powered on andinitialized. Operation proceeds from step 502 to step 504. Operationalso proceeds from step 502 to step 566 via connecting node C 564.

Returning to step 504, in step 504 the first mobile communicationsdevice, while operating in a first mode of operation, receives a timingsignal of a first type from a second mobile communications device, saidfirst type of timing signal being synchronized to a global timing signalsource. In some embodiments, the timing signal of the first type fromthe second mobile communications device communicates timing informationwhich is transmitted by the second mobile communications device afterhaving achieved synchronization with an external timing signal. In somesuch embodiments, the external timing signal is one of a globalpositioning signal, eLoran signal, LORAN-C signal, CDMA 2000 signal,WWVB signal, DTV signal and LTE signal. In some embodiments, the firstmobile communications device does not include a receiver for receivingthe external timing signal.

In various embodiments, the timing signal of the first type from thesecond mobile communications device is received in said unlicensedfrequency band. In some embodiments, the timing signal of the first typefrom the second mobile communications device is received in a beaconsignal. In some embodiments, said beacon signal communicates an 802.11beacon frame. In other embodiments, said beacon signal is a narrowbandhigh power signal. In various embodiments, said beacon signal is asignal designed to provide timing and/or frequency synchronization. Insome embodiments, the beacon signal is a WiFi compliant signal. In someembodiments, the beacon signal expressly indicates that the beaconsignal is synchronized to a global timing signal. In some suchembodiments, the global timing signal is a global positioning signal. Insome embodiments the beacon signal communicates beacon periodicityinformation. In some such embodiments, the beacon periodicityinformation is the period of the beacon signal. In various embodiments,the communicated beacon periodicity information identifies one of aplurality of predetermined alterative beacon periods. A devicerecovering the beacon periodicity information can use the beaconperiodicity information to determine sleep times and when to awake, e.g.thus conserving power. Operation proceeds from step 504 to step 506.

In step 506, the first mobile communications device synchronizes aninternal clock based on the received timing signal from the secondmobile communications device. Operation proceeds from step 506 to step508. In step 508 the first mobile communications device switches to asecond mode of operation wherein sleep state intervals in said secondmode of operation are longer in duration than sleep state intervals insaid first mode of operation. In some embodiments, sleep state intervalsin the second mode of operation are 10 times longer than sleep stateintervals in the first mode of operation. In some such embodiments,sleep state intervals in the second mode of operation are 20, 30, 40 oreven 50 times longer than sleep state intervals in the first mode ofoperation. In some embodiments, when in the second mode of operation thefirst mobile communications device has at least on average, 10 times theamount of sleep time than when in the first mode of operation. In someembodiments, the amount of sleep time when in the second mode ofoperation is at least 20, 30, 40 or even 50 times, on average, thatwhich occurs when the first mobile communications device is in the firstmode of operation. In some embodiments, the first mode of operation is afirst synchronized mode of operation, and the second mode of operationis a second synchronized mode of operation, and the first synchronizedmode of operation corresponds to a lower level of synchronization thansaid second synchronized mode of operation. Operation proceeds from step508 to step 510 and from step 508 to steps 522, 524, 528, and step 538via connecting node A 520.

Returning to step 510, in step 510 the first mobile communicationsdevice monitors for the timing signal of the first type from the secondmobile communications device. Step 510 may, and sometimes does, includestep 512 in which the first mobile communications device receives thetiming signal of the first type from the second mobile communicationsdevice. Operation proceeds from step 512 to step 514.

In step 514 the first mobile communications device is operated toproceed differently based on whether or not the timing signal of thefirst type from the second mobile communications device has beendetected by the monitoring of step 510. If the timing signal of thefirst type from the second mobile communications device has beenreceived then, operation proceeds from step 514 to step 510 foradditional monitoring and the first mobile communications device remainsin the second mode of operation. However, if the timing signal of thefirst type has not been received from the second mobile communicationsdevice in the monitoring of step 510, then operation proceeds from step514 to step 516.

In step 516 the first mobile communications device switches to the firstmode of operation. Operation proceeds from step 516 to step 518. In step518 while in said first mode of operation the first mobilecommunications device synchronizes with other devices based on secondtype timing signals. In some embodiments, a second type timing signal istiming signal, e.g., a beacon signal, which is not synchronized toglobal timing signal source. The second type timing signal, in someembodiments, may be sourced from another device or from the first mobilecommunications device. For example, if the first mobile communicationsdevice detects a first type timing signal from another device in itsvicinity, it may use that received signal for synchronization. However,if the first mobile communications device does not detect a first typetiming signal it may generate and transmit a first type timing signal,which other devices may use as a reference for synchronization. While inthe first mode of operation, the first mobile communications device, insome embodiments, monitors for first type timing signals from otherdevices. In some such embodiments, upon reception of a timing signal ofthe first type, the first mobile communications device synchronizes itsinternal clock based on the received timing signal of the first type andswitches to the second mode of operation.

Returning to step 566, in step 566 the first mobile communicationsdevice determines its current mode of operation and proceeds as afunction of the determination. If the current mode of operation is thefirst mode of operation, then operation proceeds from step 566 to step568 in which the first mobile communications device implements sleepstate intervals having a first duration. However, if the current mode ofoperation is the second mode of operation, then operation proceeds fromstep 566 to step 570 in which the first mobile communications deviceimplements sleep state intervals having a second duration, said secondduration being longer than said first duration. Operation proceeds fromstep 568 or step 570 to step 566.

Returning to step 522, in step 522 which is performed on an ongoingbasis, the first mobile communications device monitors remaining batterypower. Battery power 530 is an output of step 522.

In step 524, which is performed on an ongoing basis, the first mobilecommunications device tracks the number of timing signals of the firsttype which are being received on an ongoing basis. Step 524 includesstep 526 in which the first mobile communications device tracks thenumber of timing signals of the first type which are being received onan ongoing basis from other communications devices which aresynchronized with the external timing signal based on direct receipt ofthe external timing signal. In this exemplary embodiment, there are twosub-categories of timing signals of a first type based on whether or notthe device transmitting the first type timing signal has directlyreceived the external timing signal which is the reference sourcesignal. Number of received direct receipt based first type timingsignals 532 is an output of step 526. Number of received first typetiming signals 534 is an output of step 524.

In step 528, which is performed on an ongoing basis, the first mobilecommunications device determines the power level of received timingsignals, e.g., the power level of the most recently received timingsignal of the first type from the second mobile communications device.Received timing signal power level 536 is an output of step 528.

Returning to step 538, in step 538 the first mobile communicationsdevice determines if said second mobile communications has beensynchronized with said external timing signal based on direct receipt ofsaid external timing signal or based on a signal from anothercommunications device which received the external timing signal. In someembodiments, the basis for the timing synchronization is communicated byinformation transmitted by the second mobile communications device. Insome such embodiments, the timing signal of the first type from thesecond mobile communications device is a beacon signal which includesinformation indicating a timing synchronization basis used to controlthe transmission of the timing of the beacon signal. Step 538 includessub-step 540 in which the first mobile communications device recoversinformation indicating whether said second mobile communications deviceis synchronized with said external timing signal based on direct receiptof said external timing signal or based on a signal from anothercommunications device which received said external signal timing signal.In some embodiments, step 540 includes processing, e.g., decoding, thereceived timing signal of the first type of the second mobilecommunications device. Steps 542 and 546 are optional steps which areincluded in some embodiments. In embodiments, in which steps 542 and 546are omitted, operation proceeds from step 538 to step 544. Inembodiments, in which steps 542 and 546 are included, operation proceedsfrom step 538 to step 542.

If the determination of step 538 is that the second mobilecommunications device was synchronized with the external timing signalbased on direct receipt of the external timing signal, then operationproceeds from step 542 to step 544. In step 544 the first mobilecommunications device decides whether or not to periodically transmit atiming synchronization signal during said second mode of operation.Battery power 532, number of received direct receipt based first type oftiming signals 532, number of received first type timing signals 534 andreceived timing signal power level 536 are inputs to step 544 and usedin the decision process of step 544. In some embodiments, the decisionwhether or not to periodically transmit a timing synchronization signalis a function of remaining battery power. For example, if remainingbattery power is below a threshold the first mobile communicationsdevice decides not to transmit the timing synchronization signal. Invarious embodiments, the decision whether or not to transmit the timingsynchronization signal is a function of the strength of the timingsignal of the first type received from the second mobile communicationsdevice. For example, if the received timing signal of the first typefrom the second mobile communications device is above a certainthreshold power level, e.g., a predetermined power threshold level, thefirst mobile communications device, in some embodiments, determines notto transmit the timing synchronization signal since it is likely thatthere will be substantial overlap in the coverage areas of the timingsynchronization signal of the first type from the second mobilecommunications device and a transmitted timing synchronization signalfrom the first mobile communications device. In some embodiments, thedecision whether or not to transmit a timing synchronization signal is afunction of the number of timing synchronization signal of the firsttype being received on a periodic basis from other communicationsdevices. In some embodiments, the decision whether or not to transmit atiming synchronization signal is a function of the number of timingsynchronization signal of the first type, communicating direct receptionof the external timing signal, being received on a periodic basis fromother communications devices. Operation proceeds from step 544 viaconnecting node B 548 to step 550.

If the determination of step 544 was to transmit the timingsynchronization signal, then operation proceeds from step 550 to step552. However, if the determination of step 544 was to refrain fromtransmitting a timing synchronization signal then operation proceedsfrom step 550 to step 562. In step 562 the first mobile communicationsdevice is controlled to refrain from transmitting a timingsynchronization signal indicating synchronization with said externalsource at predetermined time intervals.

Returning to step 552, in step 552 the first mobile communicationsdevice determines the periodicity of the timing synchronization signalto be transmitted as a function of at least one of: the amount ofremaining battery power and the periodicity of timing signals of thefirst type received from the second mobile communications device. Insome such embodiments, the first mobile communications device determinesthe periodicity of the timing synchronization signal to be transmittedas a function of at least one of: the amount of remaining battery powerand the periodicity of timing signals of the first type received from aplurality of communications device including the second mobilecommunications device. In some embodiments, when the remaining batterypower is below a threshold, the first mobile communications devicetransmits at a lower frequency to conserve power than when the remainingbattery power is above the threshold. In various embodiments, there aremultiple power threshold levels corresponding to a plurality of ratetransition points. In some embodiments, the first mobile communicationsdetermines to transmit the timing synchronization signal in a mannerthat complements other received timing synchronization signals. Forexample, the first mobile communications device transmits the timingsynchronization signal at a spacing and/or interval period so as to fillin between the received timing signals of the first type from the secondmobile communications device. In some embodiments, the determination ofstep 552 includes identifying specific intervals or specific positionsin a recurring peer to peer timing structure during which the firstmobile communications device is to transmit a generated timingsynchronization signal. The timing synchronization signal is, e.g., atiming signal of the first type which does not indicate direct receptionof the external timing signal by the first mobile communications device.Operation proceeds from step 552 to step 554.

In step 554 the first mobile communications device generates said timingsynchronization signal. Step 554 includes step 556 in which the firstmobile communications device includes information indicating that saidtiming synchronization signal is based on a signal from anothercommunications device which received said external timing signal.Operation proceeds from step 554 to step 558.

In step 558 the first mobile communications device transmits thegenerated timing synchronization signal. Step 558 includes step 560 inwhich the first mobile communications device transmits informationindicating that said timing synchronization signal is based on a signalfrom another communications device which received said external timingsignal. Operation proceeds from step 558 to step 554. The transmittingof step 558 is performed at times in accordance with the determinationof step 552.

Returning to step 546, if the determination of step 538 is that thesecond mobile communication device has not been synchronized with theexternal timing signal based on direct reception of the external timingsignal, then operation proceeds from step 542 to step 546. In step 546the first mobile communications device is controlled to refrain fromtransmitting a timing synchronization signal indicating synchronizationwith said external timing source at predetermined time intervals.

FIG. 6 is a drawing of an exemplary mobile communications device 600, inaccordance with an exemplary embodiment. Exemplary mobile communicationsdevice 600 is, e.g., one of the wireless communications devices ofFIG. 1. Exemplary mobile communications device 600 may, and sometimesdoes, implement a method in accordance with flowchart 500 of FIG. 5.

Mobile communications device 600 includes a processor 602 and memory 604coupled together via a bus 609 over which the various elements (602,604) may interchange data and information. Communications device 600further includes an input module 606 and an output module 608 which maybe coupled to processor 602 as shown. However, in some embodiments, theinput module 606 and output module 608 are located internal to theprocessor 602. Input module 606 can receive input signals. Input module606 can, and in some embodiments does, include a wireless receiverand/or a wired or optical input interface for receiving input. Outputmodule 608 may include, and in some embodiments does include, a wirelesstransmitter and/or a wired or optical output interface for transmittingoutput.

Processor 602 is configured to: receive a timing signal of a first typefrom a second mobile communications device while operating in a firstmode of operation, said first type of timing signal being synchronizedto a global timing signal source; synchronize an internal clock based onthe received timing signal from the second mobile communications device;and switch to a second mode of operation wherein sleep state intervalsin said second mode of operation are longer in duration than sleep stateintervals in said first mode of operation, after synchronizing theinternal clock.

In some embodiments, said first mode of operation is a firstsynchronized mode of operation and wherein said second module ofoperation is a second synchronized mode of operation, and wherein saidfirst synchronized mode of operation corresponds to a lower level ofsynchronization than said second synchronized mode of operation. In someembodiments, said timing signal from the second mobile communicationsdevice communicates timing information which is transmitted by thesecond communications device after having achieved synchronization withan external timing signal. In various embodiments, said external timingsignal is one of a global positioning signal, eLoran signal, LORAN-Csignal, CDMA 2000 signal, WWVB signal, DTV signal and LTE signal.

Processor 602 is further configured to: determine if said secondcommunications device has been synchronized with said external timingsignal based on direct receipt of said external timing signal or basedon a signal from another communications device which received saidexternal timing signal. The basis for timing synchronization, in someembodiments, is communicated by information transmitted by said secondmobile communications device. In various embodiments, said timing signalfrom the second mobile communications device is a beacon signal whichincludes information indicating a timing synchronization basis used tocontrol the transmission timing of the beacon signal.

Processor 602 is further configured to: decide whether or not toperiodically transmit a timing synchronization signal during said secondmode of operation, when it is determined that said second communicationsdevice is synchronized with the external timing signal based on directreceipt of said external timing signal. In some embodiments, processor602 is further configured to decide whether or not to periodicallytransmit a timing synchronization signal as a function of: remainingbattery power, as part of being configured to decide whether or not toperiodically transmit a timing synchronization signal during said secondmode of operation. For example, in some embodiments, processor 602 isconfigured not to transmit the timing synchronization signal ifremaining battery power is below a threshold to conserve power. In someembodiments, processor 602 is further configured to decide whether ornot to periodically transmit a timing synchronization signal as afunction of: the strength of the timing signal received from the secondmobile communications device, as part of being configured to decidewhether or not to periodically transmit a timing synchronization signalduring said second mode of operation. For example, in some embodimentsprocessor 602 is configured not to transmit the timing synchronizationsignal if the received power level of the received timing signal fromthe second mobile communications device is above a certain threshold,e.g., a predetermined threshold level, since if it is above thethreshold it is likely that there will be substantial overlap in thecoverage area of the timing signal from the second mobile communicationsdevice and a timing synchronization signal transmitted from the firstmobile communications device. In some embodiments, processor 602 isfurther configured to decide whether or not to periodically transmit atiming synchronization signal as a function of: a number of first typetiming signals being received on a periodic basis from othercommunications devices which are synchronized with said external signalbased on receipt of said external timing signal, as part of beingconfigured to decide whether or not to periodically transmit a timingsynchronization signal during said second mode of operation. In someembodiments, processor 602 is further configured to decide whether ornot to periodically transmit a timing synchronization signal as afunction of: a number of first type timing signals being received on aperiodic basis from other communications devices, as part of beingconfigured to decide whether or not to periodically transmit a timingsynchronization signal during said second mode of operation.

Processor 602 is further configured to determine the periodicity of thetiming synchronization signal to be transmitted as a function of atleast one of: the amount of remaining battery power; and the periodicityof timing signals of the first type received from said second mobilecommunications device (e.g., transmit sync signal in a manner thatcompliments received sync signals, e.g., at a spacing and intervalperiod that fills in between signals from the second device), when it isdecided to periodically transmit a timing synchronization signal atpredetermined intervals. For example, processor 602 is configured totransmit the timing synchronization signal at a first rate when theremaining power level is below a threshold to conserve power, and totransmit the timing synchronization signal at a second rate whenremaining power level is above the threshold, wherein the first rate islower than the second rate. In some embodiments, processor 602 isconfigured to transmit the timing synchronization signal in a mannerthat complements received timing synchronization signals, e.g.,processor 602 is configured to transmit the timing synchronizationsignal at a spacing and/or at an interval period that fills in arecurring timing structure between timing signals of the first typebeing received from the second mobile communications device.

Processor 602 is further configured to: transmit information indicatingthat said transmitted timing synchronization signal is based on a signalfrom another communications device which received said external timingsignal. Processor 602 is further configured to: control said firstmobile communications device to refrain from transmitting a timingsynchronization signal indicating synchronization with said externalsignal source at predetermined time intervals during said second mode ofoperation, when it is determined that said second mobile communicationsdevice is synchronized with the external timing signal based on receiptof a timing signal from a device which did not receive said externaltiming signal.

Processor 602 is further configured to: switch back to said first modeof operation when said timing signal from the second mobilecommunications device ceases to be received.

In various embodiments, said timing signal from the second mobilecommunications device is received in said unlicensed frequency band, andprocessor 602 is configured to operate in said unlicensed frequencyband. In some embodiments, said timing signal from the second mobilecommunications device is received in a beacon signal. In some suchembodiments, said beacon signal is a WiFi compliant signal. In someembodiments, said beacon signal expressly indicates that the beaconsignal is synchronized to a global timing signal.

In some embodiments, said global timing signal is a global positioningsignal. In other embodiments, said global timing signal is an eLoransignal. In some other embodiments, said global timing signal is aLORAN-C signal. In some other embodiments, said global timing signal isa CDMA 2000 signal. In still another embodiment, said global timingsignal is a WWVB signal. In still another embodiment the global timingsignal is a DTV signal. In still another embodiment, the global timingsignal is a LTE signal.

In some embodiments, device 600 does not include a receiver forreceiving said external timing signal. In some embodiments processor 602is not configured to receive said global timing signal.

FIG. 7 is an assembly of modules 700 which can, and in some embodimentsis, used in the mobile communications device 600 illustrated in FIG. 6.The modules in the assembly 700 can be implemented in hardware withinthe processor 602 of FIG. 6, e.g., as individual circuits.Alternatively, the modules may be implemented in software and stored inthe memory 604 of the communications device 600 shown in FIG. 6. Whileshown in the FIG. 6 embodiment as a single processor, e.g., computer, itshould be appreciated that the processor 602 may be implemented as oneor more processors, e.g., computers. When implemented in software themodules include code, which when executed by the processor, configurethe processor, e.g., computer, 602 to implement the functioncorresponding to the module. In some embodiments, processor 602 isconfigured to implement each of the modules of the assembly of modules700. In embodiments where the assembly of modules 700 is stored in thememory 604, the memory 604 is a computer program product comprising acomputer readable medium comprising code, e.g., individual code for eachmodule, for causing at least one computer, e.g., processor 602, toimplement the functions to which the modules correspond.

Completely hardware based or completely software based modules may beused. However, it should be appreciated that any combination of softwareand hardware (e.g., circuit implemented) modules may be used toimplement the functions. As should be appreciated, the modulesillustrated in FIG. 7 control and/or configure the communications device600 or elements therein such as the processor 602, to perform thefunctions of the corresponding steps illustrated in the method flowchart500 of FIG. 5.

Assembly of modules 700 includes a module 704 for receiving a timingsignal of a first type from a second mobile communications device whileoperating in a first mode of operation, said first type of timing signalbeing synchronized to a global timing signal source, a module 706 forsynchronizing an internal clock based on the received timing signal fromthe second mobile communications device, and a module 708 for switchingto a second module of operation wherein sleep state intervals in saidsecond state of operation are longer in duration than sleep stateintervals in said first mode of operation. Assembly of module 700further includes a module 710 for monitoring for the timing signal ofthe first type from the second mobile communications device, a module714 for controlling operation as a function of whether or not a timingsignal of the first type was received from the second mobilecommunications device, a module 716 for switching to the first mode ofoperation when it is determined that a timing signal of the first typewas not received during monitoring, and a module 718 for synchronizingwith other devices based on second type timing signals while in saidfirst mode of operation when a timing signal of the first type is notbeing received during monitoring for timing signals of the first type.Module 710 includes a module 712 for receiving the timing signal of thefirst type from the second mobile communications device.

Assembly of modules 700 further includes a module 722 for monitoringremaining battery power, a module 724 for tracking the number of timingsignals of the first type which are being received on an ongoing basisand a module 728 for determining the power level of a received timingsignal, e.g., the most recently received timing signal of the first typefrom the second device. Module 724 includes a module 726 for trackingthe number of direct receipt based timing signals of the first typebeing received on an ongoing basis.

Assembly of modules 700 further includes a module 738 for determining ifsaid second communications device has been synchronized with saidexternal timing signal based on direct receipt of said external timingsignal or based on a signal from another communications device whichreceived said external timing signal. Module 738 includes a module 740for recovering information indicating whether said second communicationsdevice is synchronized with said external timing signal based on directreceipt of said external timing signals or based on a signal fromanother communications device which received said external timingsignal.

Assembly of modules 700 further includes a module 742 for controllingoperation as a function of whether or not said second communicationsdevice is synchronized with the external timing signal based on directreceipt of the external timing signal, a module 744 for deciding whetheror not to periodically transmit a timing synchronization signal duringsaid second mode of operation, a module 746 for controlling said firstmobile communications device to refrain from transmitting a timingsynchronization signal indicating synchronization with said externalsignal source at predetermined time intervals, a module 750 forcontrolling operation as a function of the decision whether or not totransmit a timing synchronization signal, a module 752 for determiningthe periodicity of the timing synchronization signal to be transmittedas a function of at least one of : the amount of remaining battery powerand the periodicity of timing signals of the first type received fromthe second mobile communications device, and a module 762 forcontrolling the first mobile communications device to refrain fromtransmitting a timing synchronization signal indicating synchronizationwith said external signal source at predetermined time intervals.

Assembly of module 700 further includes a module 754 for generating saidtiming synchronization signal and a module 758 for transmitting saidgenerated timing synchronization signal. Module 754 includes a module756 for including information in said timing synchronization signalindicating that said timing synchronization signal is based on a signalfrom another communications device which received said external timingsignal. Module 758 includes a module 760 for transmitting informationindicating that said timing synchronization signal is based on a signalfrom another communications device which received said external timingsignal.

Assembly of modules 700 further includes a module 766 for determiningthe current mode of operation, a module 768 for implementing sleep stateintervals having a first duration when in said first mode of operationand a module 770 for implementing sleep state intervals having a secondduration when in said second mode of operation, said second durationbeing longer than said first duration.

In various embodiments, the first mode of operation is a firstsynchronized mode of operation and the second mode of operation is asecond synchronized mode of operation and the first synchronized mode ofoperation corresponds to a lower level of synchronization than saidsecond synchronized mode of operation. In some embodiments, the timingsignal from the second mobile communications device communicates timinginformation which is transmitted by the second communications deviceafter having achieved synchronization with an external timing signal. Insome embodiments the external timing signal is one of a globalpositioning signal, a eLoran signal, a LORAN-C signal, a CDMA 2000signal, a WWVB signal, a DTV signal and an LTE signal. In someembodiments, the basis for timing synchronization is communicated byinformation transmitted by the second communications device. In someembodiments, the timing signal from the second mobile communicationsdevice is a beacon signal which includes information indicating a timingsynchronization basis used to control the transmission timing of thebeacon signal.

In some embodiments, module 744 makes its decision whether or not toperiodically transmit a timing synchronization signal during said secondmode of operation as a function of remaining battery. In someembodiments, module 744 makes its decision whether or not toperiodically transmit a timing synchronization signal during said secondmode of operation as a function of the strength of the timing signalreceived from the second mobile communications device. In someembodiments, module 744 makes its decision whether or not toperiodically transmit a timing synchronization signal during said secondmode of operation as a function of a number of first type timing signalsbeing received on a periodic basis from other communications deviceswhich are synchronized with said external signal based on receipt ofsaid external timing signal. In some embodiments, module 744 makes itsdecision whether or not to periodically transmit a timingsynchronization signal during said second mode of operation as afunction of a number of first type timing signals being received on aperiodic basis from other communications devices.

In various embodiments, the timing signal from the second mobilecommunications device is received in an unlicensed frequency band. Insome embodiments, the timing signal from the second mobilecommunications device is received in a beacon signal. In someembodiments, the timing signal from the second mobile communicationsdevice is a beacon signal. In some embodiments, the beacon signal is aWi-Fi compliant signal. In various embodiments, the beacon signalexpressly indicates that the beacon signal is synchronized to a globaltiming signal. In some such embodiments, the global timing signal is aglobal positioning signal. In some embodiments, the mobilecommunications device including assembly of modules 700 does not includea receiver for receiving said external timing signal.

Drawing 800 of FIG. 8 shows an exemplary timing structure used by anexemplary mobile communications device in a first mode of operation inwhich the mobile communications is not synchronized with respect to aglobal timing source. The exemplary timing structure of drawing 800includes peer discovery intervals and sleep intervals which areinterweaved as shown (peer discovery interval 802, sleep interval 810,peer discovery interval 812, sleep interval 820, peer discovery interval822, sleep interval 830, . . . ). Peer discovery interval 802 includes alisten portion 804, a transmit portion 806 and a listen portion 808,from the perspective of the exemplary mobile communications deviceoperating in the first mode of operation. Similarly, peer discoveryinterval 812 includes a listen portion 814, a transmit portion 816 and alisten portion 818, from the perspective of the exemplary mobilecommunications device operating in the first mode of operation.Similarly, peer discovery interval 822 includes a listen portion 824, atransmit portion 826 and a listen portion 828, from the perspective ofthe exemplary mobile communications device operating in the first modeof operation.

In some embodiments there are multiple mobile communications devicesoperating in a local peer to peer network without the benefit of anexternal global timing synchronization sources, which are operating inthe first mode of operation. In some such embodiments, one of thedevices, e.g., the first device which started the local peer to peernetwork transmits a local beacon signal which serves as a coarsesynchronization source for the other devices.

Drawing 850 of FIG. 8 shows an exemplary timing structure used by anexemplary mobile communications device in a second mode of operation inwhich the mobile communications is synchronized with respect to a globaltiming source, e.g., GPS, eLORAN, LORAN-C, CDMA2000, WWVB, DTV or LTEsource. The exemplary timing structure of drawing 850 includes peerdiscovery intervals and sleep intervals which are interweaved as shown(peer discovery interval 852, sleep interval 860, peer discoveryinterval 862, sleep interval 870, . . . ). Peer discovery interval 852includes a listen portion 854, a transmit portion 856 and a listenportion 858, from the perspective of the exemplary mobile communicationsdevice operating in the second mode of operation. Similarly, peerdiscovery interval 862 includes a listen portion 864, a transmit portion866 and a listen portion 868, from the perspective of the exemplarymobile communications device operating in the second mode of operation.

In the second mode of operation, in this exemplary embodiment, the startof the peer discovery portion is synchronized to the external timingreference signal. In addition, in this example, the end of the sleepinterval is synchronized to the external timing reference signal.External timing signal 851, e.g., a GPS signal, repeats as externaltiming signal 861 with a period 880.

When comparing operation in the first mode of operation with operationin the second mode of operation, it may be observed that sleep intervalsare longer in the second mode of operation. The higher level ofsynchronization in the second mode of operation allows for longer sleepintervals in the second mode of operation timing structure as comparedto the first mode of operation. In addition, in this example peerdiscovery intervals in the first mode of operation are longer than inthe second mode of operation. The longer sleep intervals and/or shorterpeer discovery intervals in the second mode of operation, when comparedto the first mode of operation, facilitates reduced battery consumptionin the second mode of operation in comparison to the first mode ofoperation.

FIG. 9 is a table 900 listing different exemplary timing signals thatare used in some exemplary embodiments to communicate timingsynchronization information. First row 902 describes that a firstsubtype of a first type of timing signal is a Wi-Fi compliant beaconwhich is synchronized to a global timing signal source, e.g., GPS, andis based on direct reception of the external timing signal, e.g., GPSsignal, by the device which generated and transmitted the beacon. Thefirst type, first sub-type, timing signal is generated and transmittedby a device including an external timing signal receiver, e.g.,including a GPS receiver.

Second row 904 describes that a second subtype of a first type of timingsignal is a Wi-Fi compliant beacon which is synchronized to a globaltiming signal source, e.g., GPS, but provides secondhand timinginformation about the external timing signal. The device which generatesand transmits the first type, second sub-type timing signal, did notdirectly receive the external timing signal, e.g., did not directlyreceive the GPS signal. The first type, second sub-type, timing signalis generated and transmitted by a device that does not include anexternal timing signal receiver, e.g., does not include a GPS receiver.

Third row 906 describes that a second type of timing signal is a Wi-Ficompliant beacon in which the timing reference is the reference of alocal peer device which initiated the local peer to peer network. Thesecond type of timing signal is generated and transmitted by a devicethat does not include the external timing signal receiver, e.g., doesnot include a GPS receiver.

FIG. 10 is drawing illustrating an exemplary format of an exemplarytiming signal 1000, e.g., a Wi-Fi compliant beacon. For example, theformat described with respect to FIG. 10, in some embodiments, appliesto any of the different timing signals described with respect to FIG. 9.

Exemplary timing signal 1000 includes a type identifier field 1002 andmay, and sometimes does, include one or more of optional fields (1004,1006, 1008, 1010, 1012). Type identifier field 1002 communicates whetherthe timing signal 1000 is a first type of timing signal or a second typeof timing signal. The type identifier field is used to distinguishbetween global timing synchronization and local timing synchronization.

Subtype identifier field 1004 is used when the timing signal is a timingsignal of the first type. Subtype identifier field 1004 communicatesinformation indicating whether the timing signal is based on directreception of the external signal or based on indirect secondhand timinginformation which was recovered.

Timing signal period field 1006, e.g., beacon period field, conveysinformation indicating the periodicity of the timing signal, e.g.,beacon signal. In some embodiments information in field 1006 identifiesone of a plurality of predetermined periods, e.g., 200 ms, 1 sec or 10seconds. External timing reference period 1008 conveys informationindicating the periodicity of the external timing reference signal,e.g., the periodicity of the GPS signal being used as a globalreference. External time reference type field 1010 conveys informationidentifying one of a plurality of alternative external timing referencetypes, e.g., GPS, eLoran, LORAN-C, CDMA2000 or WWVB, DTV or LTE. Timingoffset to external timing reference field 1012 conveys informationindicating the timing offset of the exemplary timing signal 1000 withrespect to the external timing reference signal.

FIGS. 11-13 provide an example in which devices without externalreference signal receivers are integrated into a peer to peer networkwhich uses an external reference signal source, e.g., GPS, as the basisfor global timing synchronization. The integration is achieved throughthe relaying of timing synchronization information. Followingintegration into the peer to peer network using the external referencesignal source the integrated devices can advantageously operate in amore efficient manner due to the higher level of synchronization, e.g.,remaining in sleep state for longer intervals and conserving batterypower.

Drawing 1100 illustrates an exemplary GPS satellite 1102, an exemplaryfirst peer to peer network 1118, an exemplary second peer to peernetwork 1120 and an exemplary third peer to peer network 1122. The GPSsatellite 1102, which is an external timing synchronization source, issometimes also referred to as a global timing source. The GPS satellite1102 generates and transmits external timing synchronization signal1128, e.g., a GPS signal. First peer to peer network 1118 issynchronized with respect to the global timing source. Peer to peernetwork 1118 includes wireless terminal A 1104 and wireless terminal B1106, each including a GPS receiver module (1124, 1126), respectively.The external timing signal 1128 from GPS satellite 1102 is received andprocessed by WT A 1104 and WT B 1106. WT A 1104 and WT B 1106synchronize with respect to the external timing synchronization sourcesignal.

Second peer to peer network includes WT F 1114, WT G 1116 and WT C 1108.In second peer to peer network WT F 1114 is generating and transmittinga 2nd type beacon signal 1144, which serves as a timing synchronizationsource for network 1120. For example, WT F 1114 may have started peer topeer network 1120 and thus serves as the local synchronization source.Second type beacon 1144 is, e.g., a second type timing signal inaccordance with row 906 of FIG. 9. In peer to peer network 1120 wirelessterminals are synchronized with respect to 2nd type beacon 1144 from WTF 1114.

Third peer to peer network includes WT D 1110, WT E 1112 and WT C 1108.In second peer to peer network WT D 1110 is generating and transmittinga 2nd type beacon signal 1142, which serves as a timing synchronizationsource for network 1122. For example, WT D 1110 may have started peer topeer network 1122 and thus serves as the local synchronization source.Second type beacon 1142 is, e.g., a second type timing signal inaccordance with row 906 of FIG. 9. In peer to peer network 1122 wirelessterminals are synchronized with respect to 2nd type beacon 1142 from WTD1110.

In this example, each of the devices (WT C 1108, WT D 1110, WT E 1112,WT F 1114 and WT G 1116) does not include a GPS receiver module, andthus devices (1108, 1110, 1112, 1114, and 1116) are unable to directlyreceive and process GPS signal 1128, the external global timingsynchronization source.

In this example, the level of timing synchronization achieved in firstnetwork 1118, is higher than the level of timing synchronizationachieved in either of the second or third peer to peer networks (1120,1122). The sleep states are longer in peer to peer network 1118, whichrelies on the external synchronization source, than in either of thepeer to peer networks (1120, 1122) which does not rely on an externalsynchronization source. In addition, the timing of peer to peer network1120 is independent of the timing of peer to peer network 1122.Therefore wireless terminal C 1108 which is participating in bothnetworks 1120 and 1122 needs to be coordinating and tracking timing forboth networks. In general, WT C 1108 remains powered on and gets lesssleep state time so that it can participate in both networks. Forexample, its needs to be powered on in discovery time intervalscorresponding to both networks.

In this example, WTs (1108, 1110, 1112, 1114, 1116) are currentlyoperating in a first mode of operation as indicated by blocks (1132,1134, 1136, 1138, 1140), respectively. WT B 1106 generates and transmits1st type beacon signal 1130 communicating that the timing informationbeing communicated is based on direct reception of external timingsignal 1128. For example, 1st type beacon signal 1130 corresponds to aformat in accordance with first type timing signal—subtype 1 asindicated by row 902 of FIG. 9. Beacon signal 1130 is in someembodiments in accordance with the format of signal 1000 of FIG. 10.Block D 1132 represents that beacon signal 1130 communicates informationthat is based on direct reception of a global timing signal by thedevice transmitting beacon signal 1130. For example, field 1004 ofbeacon signal 1130 indicates direct. Beacon signal 1130 may alsocommunicate first or global type in field 1002 and identity GPS in field1010, in addition to communicating other relevant timing information inthe other fields (1006, 1008, 1012). WT A 1104, decides not to transmita timing synchronization signal because, e.g., it is very close to WT B1106 and/or WT A 1104 has a low level of current battery power.

WT C 1108, which is in reception range of WT B 1106, receives anddetects 1st type beacon signal 1130. In some embodiments, WT C 1108monitors for 1st type beacons of the first sub-type while in the firstmode of operation during time intervals that it is being operated toreceive signals corresponding to one or more local peer to peer networksin which it is a participant, e.g., first mode discovery intervals inwhich it is listening. In some embodiments, WT C 1108 monitors for 1sttype beacons of the first type while in the first mode of operationduring additional time intervals in addition to its normal local networkoperations. For example, at a lower rate than the rate of peer discoverymonitoring in network 1120, WT C 1108 monitors for 1st type beaconsignals of the first sub-type from a network synchronized with respectto a global timing source. In this example, WT C 1108 receives 1st typebeacon 1130 and recovers the information communicated by beacon 1130.

FIG. 12 is a drawing 1200 which illustrates the propagation of timingsynchronization information. Based on received beacon 1130, WT C 1108synchronizes with respect to the global timing source. In addition, WT C1108 makes a decision to propagate timing synchronization information.For example, WT C 1108 determines that it has sufficient remainingbattery power to support transmission of a timing synchronization beacon1202. WT C 1108 also determines the rate at which to transmit beacon1202, e.g., as a function of remaining battery power. The determinationsof whether or not to transmit beacon 1202 and/or the rate oftransmission in various embodiments, are a function of other factors,e.g., the number of received beacons, the number of received beacons ofa type or sub-type, and/or the number of devices in its vicinity that itexpects would receive, would use, and/or could benefit from receivingand processing beacon 1202.

In this example, WT C 1108 decides to generate and transmit 1st typebeacon 1202. 1st type beacon 1202 communicates that the timinginformation about the external timing reference is being communicatedindirectly. WT C 1108 has not directly received and processed GPS signal1128 but is relying on timing synchronization information conveyed fromanother device, WT B 1106. For example, 1st type beacon signal 1202corresponds to a format in accordance with first type timingsignal—subtype 2 as indicated by row 904 of FIG. 9. Beacon signal 1202is in some embodiments in accordance with the format of signal 1000 ofFIG. 10. Block I 1204 represents that beacon signal 1202 communicatestiming information about the global timing reference that is based on areceived beacon signal not based on direct reception of signal 1128 byWT C 1108. For example, in beacon signal 1202 field 1004 indicatesindirect. Beacon signal 1202 may also communicate first or global typein field 1002 and identity GPS in field 1010, in addition tocommunicating other relevant timing information in the other fields(1006, 1008, 1012).

Drawing 1300 of FIG. 13 illustrates that WTs (WT D 1110, WT E 1112, WT F1114, WT G 1116) have received and processed the 1st type beacon signal1202 of the second sub-type. FIG. 13 indicates that WTs (WT C 1108, WT D1110, WT E 1112, WT F 1114, WT G 1116) transition to a second mode ofoperation as indicated by blocks (1304, 1306, 1308, 1310, 1312). In thefirst mode of operation a WT is synchronized with a local timingreference, while in the second mode of operation a WT is synchronizedwith respect to an external signal source, e.g., GPS. In addition thelevel of synchronization is higher in the second mode than in the firstmode. A wireless terminal also has longer sleep states in the secondmode than in the first mode. Based on the propagation of timinginformation regarding the external timing signal 1128, through beacon1130 and beacon 1202, wireless terminals without a GPS receiver modulehave been integrated into a network synchronized with respect to aglobal timing source. Network 1302 is an expanded peer to peer networkin which wireless terminals, e.g., mobile devices, (WT A 1104, WT B1106, WT C 1108, WT D 1110, WT E 1112, WT F 1114, WT G 1116) aresynchronized either directly or indirectly with respect to a globaltiming source, e.g. GPS. Expanded network 1302 is an expansion ofnetwork 1118 of FIG. 11. WT C 1108 is, e.g., a mobile communicationsdevice implementing a method in accordance with flowchart 500 of FIG. 5and/or implemented in accordance with FIG. 6 and/or FIG. 7.

Various method and apparatus are related to power efficient signaling,e.g. power efficient use of Wi-Fi. In various embodiments, a network,e.g., a peer to peer ad-hoc network, is synchronized to an externaltiming source. In some embodiments, a wireless communications device,e.g., a WiFi device, synchronizes to a global timing source signal,which is an out of band signal, and the wireless communications deviceuses this timing information for running certain applications, e.g.,running applications over a WiFi channel. Some wireless communicationsdevices include a receiver for receiving a global timing source signaldirectly. In various embodiments, a wireless device which receives aglobal timing signal may, and sometimes does, propagate timingsynchronization information, e.g., via a Wi-Fi beacon. Some wirelesscommunications devices which do not include a receiver for receiving theglobal timing source signal receive a Wi-Fi beacon signal communicatingtiming synchronization about the global timing signal source andsynchronize with respect to the global timing signal source based on thereceived information from the beacon. Thus some wireless communicationsdevices, e.g., high capability devices, achieve synchronization directlywith the external timing synchronization source, while other devices,e.g., lower capability device, achieve timing synchronization with theexternal timing synchronization source indirectly.

Exemplary global external timing sources are, e.g., GPS, eLoran/LORAN-C,CDMA 2000, WWVB, DTV and LTE. Some of these sources can provide accuratetiming information up to a few microseconds. Some of the sources canwork indoors as well as outdoors.

In some embodiments, after a wireless communications device obtainstiming synchronization information, it uses this global timingsynchronization in passive mode to determine when to wake up. Forexample, in one exemplary embodiment, a device will wake up everysecond, to perform certain applications. Note that each of the devicesusing this solution would wake up at the same time, since they will besynchronized to the same timing source. The examples of the applicationinclude, but are not limited to

-   -   1. Exchange peer discovery/presence information    -   2. Exchange traffic routing information (e.g. for multihop        communication)    -   3. Connection setup requests    -   4. Traffic monitoring for requests indicating intention to        transmit.

Note that these examples are applications that the device may be doingeven if it is in the sleep mode, so an efficient implementation of thesewill have an impact on the stand by time of the device.

In some exemplary implementations the timing information is obtainedfrom GPS, and the information being exchanged is peer discovery/presenceinformation. In one exemplary embodiment, the devices wake up everysecond (synchronized to the GPS second), and stay awake for certainamount of time. This time can be fixed or can depend on the interferenceenvironment seen. If there is no active connection, that the device isinvolved in, then the device goes to sleep till the next second.

In some embodiments, at least some wireless communications devices uselegacy WiFi chips and do not include a receiver to directly receive asignal from the external global signal source, e.g., the wirelesscommunications device does not include a GPS receiver module.

Some enhanced wireless communications devices with the capability toreceive the global external signal, e.g., with a GPS receiver, directlyreceive and use the external source signal, e.g., a GPS signal, tosynchronize to a global timing reference. These enhanced devices havehardware in them to acquire this timing information. After synchronizingto an external timing source, an enhanced device, in some embodiments,starts or participates in an adhoc network, e.g. an enhanced peer topeer network synchronized to the external signal source. In someembodiments, the device in the enhanced network synchronized to theglobal timing signal source uses one of more of:

-   -   pre-agreed names or SSIDs, e.g., “Globally Synced WiFi”    -   pre-agreed beacon periods, e.g., 100 ms, 1 second, 10 second    -   pre-agreed timing reference, e.g., synchronized to a GPS second

In some embodiments, devices without the global external signal receivercapability are not initially synchronized to the global time referencebut monitor for the existence of enhanced networks synchronized to aglobal timing signal source. For example, at a slower rate a devicewithout an external signal receiver, e.g., a device without a GPSreceiver, monitors for existence of enhanced networks, e.g., monitorsfor beacon signals communicating the pre-agreed upon SSIDs indicatingglobally Synced Wi-Fi. After an enhanced network has been discovered andexternal timing signal source information obtained from the receivedbeacon signal, the device can, and sometimes does join the enhancednetwork. The device without the external receiver capability can achievepower efficiency over prior operation because of the duty cycle due tobeacon periods. For example the device without the external receivercapability, when operating in a mode in which it is indirectlysynchronized to the external signal source can have less on time andmore sleep time than when in a mode in which it is not synchronized tothe external signal source. In some embodiments, when synchronized tothe external signal source the device has at least on average 10 timesthe amount of sleep time than when not synchronized to the externalsignal source. In other embodiments, the increase in sleep time is atleast 20, 30, 40 or ever 50 times on average, that which occurs when thedevice is not synchronized to the external timing signal. In variousembodiments, a device without an external signal receiver, can andsometimes does, further propagate timing information pertaining to theexternal timing signal, to other device without external signal sourcereceivers.

Note that each of the devices using this solution would wake up at thesimilar times. In various embodiments the propagation delays are minimalIn various embodiments, devices without an external signal receiver,e.g., without a GPS receiver, are synchronized indirectly to the sametiming source as devices with an external signal source receiver, e.g.,with a GPS receiver. This could enable power efficient operation forapplications such as:

-   -   1. Exchange peer discovery/presence information    -   2. Exchange traffic routing information (e.g. for multihop        communication)    -   3. Connection setup requests    -   4. Traffic monitoring for requests indicating intention to        transmit.

Note that each of these examples are applications that the device may bedoing even if it is in the sleep mode, so an efficient implementation ofthese will significantly increase the stand by time of the device.

In an exemplary implementation where the timing reference is the GPSsecond, and the beacon period is one second, the information beingexchanged is peer discovery/presence information. In this case, thedevices wake up every second (synchronized to the GPS second), and staysawake for certain amount of time. This time could be fixed or coulddepend on the interference environment seen. If there is no activeconnection, that the device is involved in, then the device goes tosleep till the next second.

One or more devices without an external signal source receiver whichparticipate in this exemplary implementation may be, and normally are,within (multihop) proximity of a device including an external signalsource receiver. Some devices without an external signal sourcereceiver, e.g., without a GPS receiver, are legacy devices which havebeen upgraded. For example, in some embodiments, firmware and/orsoftware is changed in a legacy device to configure it to listen forenhanced networks, e.g., on a slow time scale. Then after discovering anenhanced network, it may and sometimes does participate in the enhancednetwork, e.g., resulting in power efficiency.

The techniques of various embodiments may be implemented using software,hardware and/or a combination of software and hardware. Variousembodiments are directed to apparatus, e.g., mobile nodes such as mobileterminals, base stations, communications system. Various embodiments arealso directed to methods, e.g., method of controlling and/or operatingmobile nodes, base stations and/or communications systems, e.g., hosts.Various embodiments are also directed to machine, e.g., computer,readable medium, e.g., ROM, RAM, CDs, hard discs, etc., which includemachine readable instructions for controlling a machine to implement oneor more steps of a method.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an example of exemplary approaches. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

In various embodiments nodes described herein are implemented using oneor more modules to perform the steps corresponding to one or moremethods, for example, signal processing, signal generation and/ortransmission steps. Thus, in some embodiments various features areimplemented using modules. Such modules may be implemented usingsoftware, hardware or a combination of software and hardware. Many ofthe above described methods or method steps can be implemented usingmachine executable instructions, such as software, included in a machinereadable medium such as a memory device, e.g., RAM, floppy disk, etc. tocontrol a machine, e.g., general purpose computer with or withoutadditional hardware, to implement all or portions of the above describedmethods, e.g., in one or more nodes. Accordingly, among other things,various embodiments are directed to a machine-readable medium includingmachine executable instructions for causing a machine, e.g., processorand associated hardware, to perform one or more of the steps of theabove-described method(s). Some embodiments are directed to a device,e.g., communications node, including a processor configured to implementone, multiple or all of the steps of one or more methods of theinvention.

In some embodiments, the processor or processors, e.g., CPUs, of one ormore devices, e.g., communications nodes such as access nodes and/orwireless terminals, are configured to perform the steps of the methodsdescribed as being performed by the communications nodes. Theconfiguration of the processor may be achieved by using one or moremodules, e.g., software modules, to control processor configurationand/or by including hardware in the processor, e.g., hardware modules,to perform the recited steps and/or control processor configuration.Accordingly, some but not all embodiments are directed to a device,e.g., communications node, with a processor which includes a modulecorresponding to each of the steps of the various described methodsperformed by the device in which the processor is included. In some butnot all embodiments a device, e.g., communications node, includes amodule corresponding to each of the steps of the various describedmethods performed by the device in which the processor is included. Themodules may be implemented using software and/or hardware.

Some embodiments are directed to a computer program product comprising acomputer-readable medium comprising code for causing a computer, ormultiple computers, to implement various functions, steps, acts and/oroperations, e.g. one or more steps described above. Depending on theembodiment, the computer program product can, and sometimes does,include different code for each step to be performed. Thus, the computerprogram product may, and sometimes does, include code for eachindividual step of a method, e.g., a method of controlling acommunications device or node. The code may be in the form of machine,e.g., computer, executable instructions stored on a computer-readablemedium such as a RAM (Random Access Memory), ROM (Read Only Memory) orother type of storage device. In addition to being directed to acomputer program product, some embodiments are directed to a processorconfigured to implement one or more of the various functions, steps,acts and/or operations of one or more methods described above.Accordingly, some embodiments are directed to a processor, e.g., CPU,configured to implement some or all of the steps of the methodsdescribed herein. The processor may be for use in, e.g., acommunications device or other device described in the presentapplication.

While described in the context of an OFDM system, at least some of themethods and apparatus of various embodiments are applicable to a widerange of communications systems including many non-OFDM and/ornon-cellular systems.

Numerous additional variations on the methods and apparatus of thevarious embodiments described above will be apparent to those skilled inthe art in view of the above description. Such variations are to beconsidered within the scope. The methods and apparatus may be, and invarious embodiments are, used with CDMA, orthogonal frequency divisionmultiplexing (OFDM), and/or various other types of communicationstechniques which may be used to provide wireless communications linksbetween communications devices. In some embodiments one or morecommunications devices are implemented as access points which establishcommunications links with mobile nodes using OFDM and/or CDMA and/or mayprovide connectivity to the internet or another network via a wired orwireless communications link. In various embodiments the mobile nodesare implemented as notebook computers, personal data assistants (PDAs),or other portable devices including receiver/transmitter circuits andlogic and/or routines, for implementing the methods.

1. A method of operating a first mobile communications device operatingin an unlicensed frequency band, the method comprising: while operatingin a first mode of operation, receiving a timing signal of a first typefrom a second mobile communications device, said first type of timingsignal being synchronized to a global timing signal source;synchronizing an internal clock based on the received timing signal fromthe second mobile communications device; and after synchronizing theinternal clock, switching to a second mode of operation wherein sleepstate intervals in said second mode of operation are longer in durationthan sleep state intervals in said first mode of operation.
 2. Themethod of claim 1, wherein said timing signal from the second mobilecommunications device communicates timing information which istransmitted by the second communications device after having achievedsynchronization with an external timing signal.
 3. The method of claim2, wherein said external timing signal is one of a global positioningsignal, eLoran signal, LORAN-C signal, CDMA 2000 signal, WWVB signal,DTV signal and LTE signal.
 4. The method of claim 1, further comprising:switching back to said first mode of operation when said timing signalfrom the second mobile communications device ceases to be received. 5.The method of claim 1, wherein said timing signal from the second mobilecommunications device is received in said unlicensed frequency band. 6.The method of claim 2, wherein said timing signal from the second mobilecommunications device is received in a beacon signal.
 7. A first mobilecommunications device comprising: means for receiving a timing signal ofa first type from a second mobile communications device while operatingin a first mode of operation, said first type of timing signal beingsynchronized to a global timing signal source; means for synchronizingan internal clock based on the received timing signal from the secondmobile communications device; and means for switching to a second modeof operation, wherein sleep state intervals in said second mode ofoperation are longer in duration than sleep state intervals in saidfirst mode of operation, after synchronizing the internal clock.
 8. Thefirst mobile communications device of claim 7, wherein said timingsignal from the second mobile communications device communicates timinginformation which is transmitted by the second communications deviceafter having achieved synchronization with an external timing signal. 9.The first mobile communications device of claim 8, wherein said externaltiming signal is one of a global positioning signal, eLoran signal,LORAN-C signal, CDMA 2000 signal, WWVB signal, DTV signal and LTEsignal.
 10. The first mobile communications device of claim 7, furthercomprising: means for switching back to said first mode of operationwhen said timing signal from the second mobile communications deviceceases to be received.
 11. The first mobile communications device ofclaim 7, wherein said timing signal from the second mobilecommunications device is received in said unlicensed frequency band. 12.The first mobile communications device of claim 8, wherein said timingsignal from the second mobile communications device is received in abeacon signal.
 13. A computer program product for use in a first mobilecommunications device, the computer program product comprising: acomputer readable medium comprising: code for causing at least onecomputer to receive a timing signal of a first type from a second mobilecommunications device while operating in a first mode of operation, saidfirst type of timing signal being synchronized to a global timing signalsource; code for causing said at least one computer to synchronize aninternal clock based on the received timing signal from the secondmobile communications device; and code for causing said at least onecomputer to switch to a second mode of operation wherein sleep stateintervals in said second mode of operation are longer in duration thansleep state intervals in said first mode of operation, aftersynchronizing the internal clock.
 14. The computer program product ofclaim 13, wherein said timing signal from the second mobilecommunications device communicates timing information which istransmitted by the second communications device after having achievedsynchronization with an external timing signal.
 15. The computer programproduct of claim 14, wherein said external timing signal is one of aglobal positioning signal, eLoran signal, LORAN-C signal, CDMA 2000signal, WWVB signal, DTV signal and LTE signal.
 16. A first mobilecommunications device comprising: at least one processor configured to:receive a timing signal of a first type from a second mobilecommunications device while operating in a first mode of operation, saidfirst type of timing signal being synchronized to a global timing signalsource; synchronize an internal clock based on the received timingsignal from the second mobile communications device; and switch to asecond mode of operation wherein sleep state intervals in said secondmode of operation are longer in duration than sleep state intervals insaid first mode of operation, after synchronizing the internal clock;and memory coupled to said at least one processor.
 17. The first mobilecommunications device of claim 16, wherein said timing signal from thesecond mobile communications device communicates timing informationwhich is transmitted by the second communications device after havingachieved synchronization with an external timing signal.
 18. The firstmobile communications device of claim 17, wherein said external timingsignal is one of a global positioning signal, eLoran signal, LORAN-Csignal, CDMA 2000 signal, WWVB signal, DTV signal and LTE signal. 19.The first mobile communications device of claim 16, wherein said atleast one processor is further configured to: switch back to said firstmode of operation when said timing signal from the second mobilecommunications device ceases to be received.
 20. The first mobilecommunications device of claim 17, wherein said timing signal from thesecond mobile communications device is received in said unlicensedfrequency band.